Who this is for: Cambridge IGCSE Economics (0455) students who want supply — the law of supply, supply curves and the difference between movements and shifts — to become a reliable source of marks instead of a mirror image of demand they apply without thinking.
What query it owns: how to understand and revise supply in Cambridge IGCSE Economics.
Why this is safe: this page owns the supply revision-guide angle, while Tutopiya’s Supply subtopic page owns the learning resource and the free Supply quiz owns the practice.

Supply is the quantity of a good or service producers are willing and able to sell at each price over a given time period. Cambridge IGCSE Economics (0455) expects you to state the law of supply, draw upward-sloping supply curves, and distinguish a movement along the curve (caused by price change) from a shift (caused by changes in costs, technology, taxes or subsidies). This guide links each idea to the diagram questions examiners set.

Key takeaways

• The law of supply states that, ceteris paribus, as price rises, quantity supplied rises — and vice versa.
• A supply curve slopes upward from left to right (positive price–quantity relationship).
• A movement along the supply curve is caused by a change in the good’s own price.
• A shift of the supply curve is caused by non-price factors (costs of production, technology, indirect taxes, subsidies).
• Extension of supply = price rises, quantity supplied rises; contraction = price falls, quantity supplied falls.

What is supply in Cambridge IGCSE Economics?

Supply is the quantity of a product that producers are willing and able to offer for sale at various prices during a specific period. Cambridge IGCSE Economics (0455) tests whether you can define supply precisely, draw an accurate upward-sloping curve, and explain how production costs and government policy shift supply at every price level.

You can read the full explanation, diagrams and notes on Tutopiya’s Supply subtopic page before you attempt questions.

Core supply definitions you must know

Term	Definition	Diagram signal
Supply	Quantity producers are willing and able to sell at each price	Entire curve or schedule
Quantity supplied	Amount sold at one specific price	A single point on the curve
Law of supply	Price and quantity supplied move in the same direction	Upward-sloping curve
Extension of supply	More sold because own price rose	Movement up along the curve
Increase in supply	More sold at every price (non-price factor)	Curve shifts right

How to analyse supply — step by step

1. Draw axes — price on the vertical axis, quantity on the horizontal axis.
2. Plot the supply curve — upward-sloping, labelled S.
3. Identify the cause — has the good’s own price changed, or a non-price factor?
4. If own price changed — show a movement along (extension or contraction).
5. If a non-price factor changed — draw a parallel shift (increase = right; decrease = left).
6. Link to costs — higher production costs shift supply left; lower costs shift supply right.

Test yourself with the free Supply quiz once you can separate movements from shifts every time.

Movement along vs shift of supply: the comparison that wins marks

Change	Cause	Diagram	Terminology
Movement along	Change in the good’s own price	Slide along existing S curve	Extension (price ↑) or contraction (price ↓)
Shift right	Non-price factor reduces costs or improves conditions	Whole curve moves right	Increase in supply
Shift left	Non-price factor raises costs or worsens conditions	Whole curve moves left	Decrease in supply

Non-price factors that shift supply

Factor	Increase in supply (shift right)	Decrease in supply (shift left)
Costs of production	Costs fall (cheaper raw materials, wages)	Costs rise
Technology	Improved technology lowers unit costs	—
Indirect taxes	Tax removed or reduced	Tax imposed or increased
Subsidies	Subsidy granted to producers	Subsidy removed
Weather (agriculture)	Good harvest	Poor harvest, drought

Supply in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical supply stem
Define	Precise economic meaning	”Define supply.”
Draw	Accurate labelled diagram	”Draw a supply curve for product Y.”
Distinguish between	Clear comparison	”Distinguish between an increase in supply and an extension of supply.”
Explain	Cause and effect	”Explain the effect of an increase in production costs on supply.”
Analyse	Break down with diagrams	”Analyse the effect of a subsidy on the market for solar panels.”

Worked exam-style stems (how to answer the wording)

1. “Define supply.” Supply is the quantity of a good or service that producers are willing and able to sell at each price over a given time period. Mark-scheme reward: willing + able + at each price.
2. “The price of wheat rises. Explain the effect on the quantity supplied of wheat.” Higher price causes an extension of supply — a movement up along the existing supply curve, so farmers supply more wheat. Reward: extension + movement along (not a shift).
3. “The cost of fertiliser increases. Explain the effect on the supply of wheat.” Higher production costs decrease supply at every price — the supply curve shifts to the left. Less wheat is supplied at each price because farming is more expensive. Reward: shift left + link to costs.

How supply connects to the rest of Cambridge IGCSE Economics

Supply pairs with Demand to determine Market Equilibrium. The Cambridge IGCSE Economics resource hub links every Allocation of Resources subtopic.

Common mistakes students make

• Confusing a cost increase (shifts supply left) with a price increase (movement up along the curve).
• Using “supply rises” when only quantity supplied changes.
• Drawing a downward-sloping supply curve (violates the law of supply).
• Forgetting that a subsidy increases supply (shifts right) and an indirect tax decreases supply (shifts left).
• Mixing up extension (price rises) with increase in supply (shift right).

When you need more support

If supply diagram questions keep costing marks, work through the Supply quiz, then get focused help from a Cambridge IGCSE Economics tutor.

Frequently asked questions

Is supply hard in Cambridge IGCSE Economics? The law of supply is simple. Marks are lost mainly by confusing cost-driven shifts with price-driven movements along the curve.

What is the law of supply? Ceteris paribus, as the price of a good rises, the quantity supplied rises, and vice versa.

What causes a shift in supply? Non-price factors: costs of production, technology, indirect taxes, subsidies and weather (for agricultural goods).

How do I revise supply effectively? Practise diagram labelling, link each shift factor to left or right, then take the Supply quiz.

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